Silicone rubber compositions of the type comprising vinylpolysiloxane and hydrogen polysiloxane which are heat cured through hydrosilation in the presence of a platinum catalyst are known in the art. Because of their self adhesion, they are often used as protective coating compositions for electric and electronic parts and adhesive as compositions for bonding electric and electronic parts to substrates. The prior art silicone rubber compositions of this type, however, are not necessarily fully adhesive to various substrates, especially to metallic, ceramic, and plastic substrates.
It was proposed in Japanese Patent Publication Nos. 13508/1978 and 5836/1982 to add various adhesive aids such as hydrogenpoly-siloxanes having an epoxy or alkoxy group, alkoxysilanes or hydrolyzates thereof to these silicone rubber compositions in order to improve their adhesion to various substrates. Despite the addition of these adhesive aids, it is necessary to cure these silicone rubber compositions at minimum temperatures of 100.degree. to 120.degree. C. in order to obtain improved adhesion to the substrate. This is because the adhesion of such compositions depends largely on the curing temperature. Thus, curing at relatively low temperatures of less than 100.degree. C. often results in unsatisfactory adhesion. Therefore, if the silicone rubber compositions used as adhesives for electric and electronic parts are cured at relatively low temperatures, there can be gaps in the adhesion between the composition and the part. These non-adhered gaps can allow moisture and contaminants to penetrate which results in part corrosion and deteriorated insulation.
In addition, low-temperature bonding requirements are increasing in recent years as a new application or for energy saving. There is a need for a silicone rubber composition capable of low-temperature curing to provide improved adhesion.